Chapter 2: Host Parasite Interactions

Question 1

Origins of Microbiota: Fetus

Answer 1

Sterile until birth, exposure to environment leads to colonization

Question 2

Symbiosis:

Answer 2

Two organisms living together

Question 3

Commensalism:

Answer 3

One organism benefits, other is unharmed

Question 4

Mutualism:

Answer 4

Microorganism and host benefit

Question 5

Parasitism:

Answer 5

One organism benefits while the host is harmed

Question 6

Indigenous microbiota:

Answer 6

Microbes commonly found on or in healthy persons

Question 7

Resident microbes:

Answer 7

Colonize area for months or years

Question 8

Transient microbes:

Answer 8

Temporarily colonizing host

Question 9

Carrier state:

Answer 9

Pathogenic organism establish themselves in host without symptoms

Question 10

Factors That Determine the Composition of
the Usual Microbial Biota:

Answer 10

1. Specific nutritional factors at that location
2. Antibacterial substances that naturally occur (bile, lysozyme, fatty acids)
3. Environmental factors (pH, moist or dry, gas atmosphere)
4. Changes due to age, nutritional status, disease state, and drug therapy

Question 11

Normal microbiota:

Answer 11

Significant role in providing host resistance to
infections

• Change in environmental conditions may predispose an individual to infection by the normal microbiota (opportunistic infection)
• A Clinical Microbiologist should be able to
  recognize and identify the types of microorganisms found at various body site

Question 12

Normal Microbiota: Skin

Answer 12

• Generally superficial organisms
  – Skin surface and hair follicles
  – Scrub 90% away by washing
  – Composition depends on activity
  of sebaceous or sweat glands
  – Skin has shedding mechanism
• Apocrine sweat glands
  – Secrete substances metabolized
  by bacteria (especially armpit, groin, and
  perineum)
• Release of odorous amines

Question 13

Normal Microbiota: Mouth

Answer 13

• Streptococcus predominates
• Plaque (Biofilm) - Low oxidation reduction potential so anaerobes grow
• Buccal mucosa and tooth surface
  – Production of acids by
  microorganisms, leading to tooth decay

Question 14

Upper respiratory tract:

Answer 14

Mouth, nasopharynx, oropharynx, larynx

• colonized by viridans streptocci

Question 15

Lower respiratory tract:

Answer 15

Trachea, bronchi, pulmonary parenchyma

-protected by ciliary epithelial cells and mucus, normally considered sterile

Question 16

GI tract:

Answer 16

Comprises esophagus, stomach, small intestine, and colon

Question 17

Stomach is low in microbes due to pH=2, what are some exceptions?

Answer 17

– Some Streptococcus, Enterococcus, Prevotella and H. pylori can live here

– Endospores, parasitic cysts, and microbes enmeshed in food - Escape stomach and enter the intestine

Question 18

Colon has largest number of microbes in GI tract:

Answer 18

– 10^12 bacteria per gram of solid material
– contains over 70% of all microbes in the body.
– Most are obligate anaerobes
– Many use pili to hold

Question 19

Antibiotics affect:

Answer 19

Can change usual biota. Can cause severe necrotizing enterocolitis, diarrhea, or superinfection.

Question 20

Sterile sites in GU tract:

Answer 20

Kidneys, bladder, cervix, and fallopian tubes

Question 21

Nonsterile sites of GU tract:

Answer 21

Distal centimeter of urethra, vagina

Question 22

Opportunistic infections:

Answer 22

Cause disease when habitat is changes, may occur due to weak immune system.

Question 23

Immunosuppression caused by:

Answer 23

– Immunosuppressive drugs
– Chemotherapy
– Radiation
– Immune defects

Question 24

The normal microbiota benefits the host by ___

Answer 24

Priming the immune system, outcompeting potential pathogens for nutrients, and creating a hostile environment for other microbes.

Question 25

Pathogenicity:

Answer 25

Ability of an organism to produce disease

Question 26

Opportunistic pathogens:

Answer 26

Usually do not cause infection unless special circumstance such as invasive medical procedures, immunosuppressed person, etc

Question 27

True pathogens:

Answer 27

Organism that cause disease in healthy immunocompetent hosts, cause disease a high percentage of the time

Question 28

Iatrogenic infection:

Answer 28

Occurs as a result of medical treatment or procedure

Question 29

Direct transmission:

Answer 29

Congenital contact, close contact (salivary, skin), droplet infection

Question 30

Indirect transmission:

Answer 30

Fomites, water, food, airborne, cuts/bites. arthropods

Question 31

Zoonoses:

Answer 31

Contact with animals or animal products

Question 32

Incidence:

Answer 32

Refers to number of individuals infected in a population

Question 33

Prevalence:

Answer 33

Percentage of infected in a given population at a given time

Question 34

Endemic:

Answer 34

Disease is consistently present in given location

Question 35

Epidemic:

Answer 35

Larger numbers of cases of disease in given location

Question 36

Pandemic:

Answer 36

Epidemic around the world

Question 37

Infection vs Disease:

Answer 37

Infection: invasion and replication of pathogens within the body Disease: condition that impairs normal functioning and typically has signs, symptoms

Question 38

Virulence:

Answer 38

Relative ability of microbe to cause disease, measured by number of organism required to cuase infection in host

Question 39

Virulence factors:

Answer 39

Traits that allow microbe to persist in a host and cause disease * Resist phagocytosis * Toxins and extracellular enzymes * Adhesive fimbriae and pili

Question 40

Prevention of phagocytosis:

Answer 40

Capsule (masks cell surface structures) Protein A (interferes with binding of host antibodies, binds Fc portion of IgG)

Question 41

Panton-Valentine leukocidin:

Answer 41

Killing of phagocytes, causes discharge into cytoplasm and kills cell

Question 42

Adhesins:

Answer 42

Surface polysaccharides, fimbriae/pili in bacteria - enable attachment to host surface structure to increase ability to colonize

Question 43

Break antibody:

Answer 43

IgA protease

Question 44

Hide from antibody:

Answer 44

Change surface antigen

Question 45

Invasion:

Answer 45

Penetrate and grow in tissues

Question 46

Dissemination:

Answer 46

Spread to distant sires in body

Question 47

Exotoxins:

Answer 47

Both gram negative and positive cells – Secreted by cell or released with cell lysis – Have enzyme activity and specificity in activity – Potent – Destroyed by heat - Binding subunit and toxic subunit

Question 48

Endotoxins:

Answer 48

LPS, cell wall component of gram-negative bacteria - O-specific polysaccharide-core-lipid A Toxin activity: Lipid A Effects: hypotension, fever, initiates coagulation

Question 49

Host Resistance Factors: physical barriers

Answer 49

Intact skin is effective against most pathogens

Question 50

Host Resistance Factors: cleansing mechanisms

Answer 50

Desquamation of skin, movement of liquids (tears, urine), cilia

Question 51

Host Resistance Factors: low pH

Answer 51

stomach, vagina

Question 52

Host Resistance Factors: antimicrobial substances

Answer 52

- fatty acids on skin - HCl in stomach - lysozymes that hydrolyze peptidoglycan - IgA, antibody found in saliva, secretions - low molecular weight cationic proteins such as beta-lysins - interferons that inhibit viral replication

Question 53

Phagocytic cells:

Answer 53

Engulf and digest lysosomes *neutrophils, macrophages, monocytes

Question 54

Steps of phagocytosis:

Answer 54

1. chemotaxis 2. attachment 3. ingestion 4. killing

Question 55

Inflammation:

Answer 55

Nonspecific response to injury or foreign body. Chemical mediators increases blood flow causing erythema, edema, heat, and pain due to swelling *increased WBC counts resulting in purulence

Question 56

Innate immunity:

Answer 56

Natural or nonspecific immunity 1. physical or chemical barriers such as skin or mucous membranes 2. blood proteins that act as mediators of infection 3. little or no specificity

Question 57

Adaptive/specific immunity:

Answer 57

Passive vs. Active Humoral vs. Cell-mediated Highly specialized vs. develop memory

Question 58

Lymphocytes (adaptive immunity)

Answer 58

B cells: antibodies T cells : T-helper or cytotoxic T-cells

Question 59

Mechanisms by Which Microbes May Overcome the Host Defenses:

Answer 59

1. Induce immune tolerance (not recognize pathogen as foreign) 2. Immune suppression (actively destroy immune response) 3. Antigenic variation 4. Intracellular "hiding"